A chimney draft system can, in principle, be located anywhere in the flow path of the flue gases from the flue gas outlet of the fireplace to the outlet end of the chimney. It is common to arrange a chimney draft system at the outlet end of the chimney, where the temperature of the flue gases is the lowest, and it will often be possible and relatively simple to retrofit a chimney draft system at this location. Flue gases can be very hot, and although some cooling will take place on their way from the fireplace to the outlet of the chimney, the flue gases can still be hot when leaving the outlet of the chimney. Chimney draft system including its motor must therefore be constructed to operate at elevated temperatures caused by the flue gases.
EP 0 053 703 discloses a chimney draft system with an impeller, for mounting at the flue gas outlet of a furnace. U.S. Pat. No. 4,236,443 discloses a chimney draft system for mounting directly above the chimney mouth. Each of these systems has a motor with a motor shaft carrying an impeller at its distal end, and the distal end of the motor shaft will come into contact with the hot flue gases, and heat will be conducted through the motor shaft to the motor whereby the motor will be heated. Motors need to be constructed to resist such heating which makes the motors more expensive.
It is an object of the invention to provide an impeller for a motor-driven chimney draft system which reduces the heat transfer from the hot flue gases in the chimney to the motor.